title: Age-resolving osteopetrosis: a rat model implicating microphthalmia and the related transcription factor TFE3.
abstract: Microphthalmia (Mi) is a basic helix-loop-helix-leucine zipper (b-HLH-ZIP) transcription factor implicated in pigmentation, mast cells, and bone development. Two dominant-negative mi alleles (mi/mi and Mior/Mior) in mice cause osteopetrosis. In contrast, osteopetrosis has not been observed in a number of recessive mi alleles, suggesting the existence of Mi protein partners important in osteoclast function. An osteopetrotic rat of unknown genetic defect (mib) has been described whose skeletal sclerosis improves dramatically with age and that is associated with pigmentation defects reminiscent of mouse mi alleles. Here we report that this rat strain harbors a large genomic deletion encompassing the 3' half of mi including most of the b-HLH-ZIP region. Osteoclasts from these animals lack Mi protein in contrast to wild-type rat, mouse, and human osteoclasts. Mi is not detectable in primary osteoblasts. In addition TFE3, a b-HLH-ZIP transcription factor related to Mi, was found to be expressed in osteoclasts, but not osteoblasts, and to coimmunoprecipitate with Mi. These results demonstrate the existence of members of a family of biochemically related transcription factors that may cooperate to play a central role in osteoclast function and possibly in age-related osteoclast homeostasis.
authors.affiliation: Dana Farber Cancer Institute, Department of Pediatric Oncology, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: K N
authors.initials: KN
authors.lastname: Weilbaecher
authors.forename: C L
authors.initials: CL
authors.lastname: Hershey
authors.forename: C M
authors.initials: CM
authors.lastname: Takemoto
authors.forename: M A
authors.initials: MA
authors.lastname: Horstmann
authors.forename: T J
authors.initials: TJ
authors.lastname: Hemesath
authors.forename: A H
authors.initials: AH
authors.lastname: Tashjian
authors.forename: D E
authors.initials: DE
authors.lastname: Fisher
mesh_terms: D000818:Animals; D001483:Base Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000502:physiology*; D015870:Gene Expression; D018257:Helix-Loop-Helix Motifs; D006801:Humans; D016350:Leucine Zippers; D051379:Mice; D051739:Microphthalmia-Associated Transcription Factor; D008850:Microphthalmos / Q000235:genetics*; D008969:Molecular Sequence Data; D010006:Osteoblasts / Q000378:metabolism; D010010:Osteoclasts / Q000502:physiology*; D010022:Osteopetrosis / Q000209:etiology*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D011922:Rats, Mutant Strains; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid; D014157:Transcription Factors / Q000502:physiology*
chemical_list: D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; C497234:MITF protein, human; D051739:Microphthalmia-Associated Transcription Factor; C497235:Mitf protein, mouse; C497236:Mitf protein, rat; D012333:RNA, Messenger; C069203:TFE3 protein, human; D014157:Transcription Factors